Converting to dual alternators

[plym49]

i wonder how much HP , running all that dual alt stuff takes from the engine. I would guess using math one could pall park it.

Power still being power, you can estimate it. One horsepower equals 746 watts. In DC circuits, power (watts) equals the volts times the amps.

Obviously, your alternator is not putting out full output all the time. So usually you would calculate the normal running requirements of your vehicle. You can measure this with an ammeter or estimate based on the types of circuits and equipment you run.

Just to use round numbers, let's say that your vehicle requires an average of 20 amps steady-state to run. 20 amps times 28 volts equals 560 watts.

560 watts divided by 746 watts per hp equals 3/4 of a horsepower.

But we are not done. The alternator is not 100% efficient and there are parasitic losses (fan belt, windage, etc.). A ballpark is to assume 80% efficiency. This puts you right up around 1 hp.

Obviously, the amperage numbers above are illustrative but the 746 watts per hp is 'the law' and the 80% efficiency is a reasonable estimate.

To get an idea of the relationships involved, look at the engine hp ratings for gensets of a given wattage capacity.

 

[LowTech]

Dug another thing you can do when you have a separate 12 volt system with its own dedicated battery..Is you can use one of those cheap 12 volt solar chargers so you can go longer times before you even need to start the truck to charge the acc battery..Having a separate 12 system allows you to run things like dual power fridges.,and any other item you would find in an rv.

We did that one too. HF had a 45 watt panel kit, charge controller w/ diff volt output ports, and some odds and ends. Same cheap kit I run on my van. Had a frame made so that I could attache the whole thing to the fork mounts for our bikes on the rack. Wired the panels together and into a trailer plug.
It lets me take the whole frame of panels off one rig and put it on another (from van to 109), or set it out in the sun and run an extension cable. When we did the trip this summer we just carried the panels, in frame, on the 105. When we were going to camp for a bit we would off-load the bikes, clamp the frame to the bike mounts on our cab-over rack, and plug it in.

We just bought the second kit, it was on sale before christmas, . . . think we paid like $150 for it. Will frame and mount this set between the branch-shedding roof rails on the box.
We don't really run much on DC, some lights, a couple case fans, music , some laptop and cell charging. 45 watts work fine till I find a real good deal at some future time.

 

[DUG]

Power still being power, you can estimate it. One horsepower equals 746 watts. In DC circuits, power (watts) equals the volts times the amps.

Obviously, your alternator is not putting out full output all the time. So usually you would calculate the normal running requirements of your vehicle. You can measure this with an ammeter or estimate based on the types of circuits and equipment you run.

Just to use round numbers, let's say that your vehicle requires an average of 20 amps steady-state to run. 20 amps times 28 volts equals 560 watts.

560 watts divided by 746 watts per hp equals 3/4 of a horsepower.

But we are not done. The alternator is not 100% efficient and there are parasitic losses (fan belt, windage, etc.). A ballpark is to assume 80% efficiency. This puts you right up around 1 hp.

Obviously, the amperage numbers above are illustrative but the 746 watts per hp is 'the law' and the 80% efficiency is a reasonable estimate.

To get an idea of the relationships involved, look at the engine hp ratings for gensets of a given wattage capacity.

Couldn't I just turn up the fuel until flames shoot out of the stack and fill the crankcase full of Lucas to overcome the tremendous drag of the second alt?

 

[militarysteel]

probably not, but yes you are mostly intellectually challenged.

Couldn't I just turn up the fuel until flames shoot out of the stack and fill the crankcase full of Lucas to overcome the tremendous drag of the second alt?

 

[DUG]

probably not, but yes you are mostly retarded.

Well coming from you that means nothing.

Odd how you can spell retarded but not deuce. My guess is you are more familiar with the word.

 

[doghead]

Guys, the Federal Government has mandated that word no longer be used. The new term is "Intellectually Challenged". It's called Rosa's law.

The term has been wrongly used and offending many people for a long time. Please refrain from using it on this website.




lastly, personal insults are not allowed in the forums.

Dug, pop an extra pill

MS, get some pills

 

[DUG]

Guys, the Federal Government has mandated that word no longer be used. The new term is "Intellectually Challenged". It's called Rosa's law.

The term has been wrongly used and offending many people for a long time. Please refrain from using it on this website.




lastly, personal insults are not allowed in the forums.

Dug, pop an extra pill

MS, get some pills

Three more Valium washed down with a shot of rum. I'm ready to discuss Harry Potter trains with triple alts now.

 

[doghead]

Wow, somebody actually took my instructions seriously.

We'll get you through this Dug.

Rat, 52 more posts 'til 200...

 

[DUG]

Wow, somebody actually took my instructions seriously.

We'll get you through this Dug.

Rat, 52 more posts 'til 200...

I listen cuz you ain't got no fancy book learnin', you gots real world, been there done that wouldn't even wear the t shirt exerperence.

Rat ain't answering my texts so he must be in his fancy school getting his 3rd or 4th degree or at one of his J O B s.

I'm on Christmas "stand down". That's chilling and getting paid, WITHOUT taking leave. Good times......................

 

[Westech]

you know no one has talked about pulley size and alternator speed. That 12V alternator you could run one large pulley to just idle it along.. no need to spin it at 50000000 RPM.

 

[DUG]

you know no one has talked about pulley size and alternator speed. That 12V alternator you could run one large pulley to just idle it along.. no need to spin it at 50000000 RPM.

How much power do we think the second alt is costing me? Not enough for me to notice while driving yet. Sure can't hurt the fuel mileage much.

I'm just guessing here, but I'm thinking the 12 volt battery will stay pretty much topped off 90% of the time and the 12 volt alt won't be too much of a drag.

I would bet that the 12 volt alt add on is less of a drag than the winch I added on front, the towbar I put in the back or the four jerry cans that are sometimes full.

Again, just guessing, but I don't think the deuce is even gonna notice it's there. If I'm wrong I'll report back.

 

[Westech]

I not saying slow it down to save engine power....... just ware and tare on the alternator. A Alternator will only have so Many RPMS in its life...... just saying if you can cut the speed in half maybe it would last a little longer. Like you said its not going to be doing much of anything as is.

 

[doghead]

remember Westy, the ldt is actually running about half the speed of a gas engine.

 

[Westech]

not at speed.... its running about 500 + more RPM then the "GM" car of the day

 

[rat4spd]

Wow, somebody actually took my instructions seriously.

We'll get you through this Dug.

Rat, 52 more posts 'til 200...

You can't say I'm not aiming high eh DH?

As for the word that "Intelectually challenged" has been mandated to replace, Dug and I had a brother with Down's. He made it to about 24 years old, so we are familiar with that word.

 

[plym49]

you know no one has talked about pulley size and alternator speed. That 12V alternator you could run one large pulley to just idle it along.. no need to spin it at 50000000 RPM.

At the risk of bringing some of the comments back down to reality, actually, not.

Alternators will not generate their full output unless they are spinning at 5000 to 6000 rpm. That's why they have overdriven pulleys.

Some alts generate more at idle than others. In general, the higher the output of the alternator the more it will produce when the motor is idling.

 

[plym49]

How much power do we think the second alt is costing me? Not enough for me to notice while driving yet. Sure can't hurt the fuel mileage much.

I'm just guessing here, but I'm thinking the 12 volt battery will stay pretty much topped off 90% of the time and the 12 volt alt won't be too much of a drag.

I would bet that the 12 volt alt add on is less of a drag than the winch I added on front, the towbar I put in the back or the four jerry cans that are sometimes full.

Again, just guessing, but I don't think the deuce is even gonna notice it's there. If I'm wrong I'll report back.

I don't think you will notice much difference. You are probably not trolling for fuel mileage anyway: you have so much going against you fuel-mileage wise to begin with, the extra alt is not going to be noticed much.

If you notice a difference, there are things you can do. You can get larger pulleys but these are really for the drag race boys. You will be working against what you want to achieve, which is a dependable 12 volts for your toys with the motor mostly idling.

More realistic would be to install a switch in series with the sensor wire (you will need an alternator with a separate (ie, not internal) sensor wire for this trick to work). By opening the connection the alt will not charge. The parasitic losses are not too much more than an idler pullley (well, not quite as little because of the overspeed, mass of the rotor and the alternator fan). But a lot less than it charging.

Given the low rpm nature of your motor, I would be surprised if you observed a significant untoward effect from just hooking it up regular and forgetting about it.

 

[plym49]

42 to go - don't think we're gonna make it.

 

[JasonS]

Looks like I went home just when the party was getting going.....

There were a lot of comments about how which alternator "knows" to charge which battery. In short, the alternators have NO idea what is attached. They simply try to maintain full output voltage until the internal impedance causes the voltage to drop under high load. It doesn't need to know. It also doesn't have to be super accurate. Your "28V" is a rough guess at the appropriate charging voltage anyway. It certainly isn't correct over the normal operating temperature range of the vehicle.

As long as the battery terminal voltage (lets say 14V) is above the battery open circuit voltage (say 12.8V), ALL the power delivered to your 12V load is generated by the alternator. Absolutely NONE is supplied by the battery and the battery is maintained at the proper voltage of 14V. Same with the 28V side of things.

Lets say that the lower battery tends to be on the low side. Adding a 14V source (alt or equal) will bring it up to normal. If the lower battery is high, nothing happens; current will not flow from a 14V source to a 14.5V battery.

 

[DUG]

not at speed.... its running about 500 + more RPM then the "GM" car of the day

Oh, I get it now. I thought we we worried about it dragging the mighty deuce down. I shoulda spent the extra 10 and got the lifetime warranty. Now that I have a core, a replacement is less than 40 bucks. I might be cheaper to get a spare alt than to replace the pulley.

I've already decided to spend the $123 for another 24 volt alt. Just to keep handy. Of course I'm the guy who has a spare dogbone and bracket in the tool box.